I understand your Printer is offline on your Windows 8 computer.
The easiest thing to do is just rebooted everything. Turn off router, computer and printer.
Wait a few minutes and turn on router, computer and printer.
Before trying to print make sure there is nothing waiting to be printed. Right click on your printer and see whats printing. Remove if anything there. Try to print again.
If the printer still showing offline try installing and running HP Print and Scan Doctor.
Download and install at this location.http://h10025.www1.hp.com/ewfrf/wc/softwareDownloadIndex?cc=us&lc=en&jumpid=ex_r4155/hho/ipg/ccdoc/p...
Let me know how this goes.
Thanks